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The confrontation played out while security cameras rolled: A police officer repeatedly hit a man who had pushed him, the blows continuing even after the man was handcuffed on the floor of an apartment-building elevator.

Prosecutors say the video shows that Officer David London summarily assaulted Iraq war veteran Walter Harvin. Then London lied to cover up the attack, prosecutors said as London's criminal trial opened Friday.

But London's lawyer said the silent video doesn't tell jurors everything they need to know about the July 2008 incident, arguing that the officer used justifiable force.

London's case marks the second police-conduct trial in as many months in the city to focus on videotapes and debate whether they provide a full picture.

In April, former NYPD rookie Patrick Pogan was convicted of lying about his Times Square encounter with a bike-riding activist, but Pogan was cleared of assault and harassment charges. A tourist videotaped the incident, also in July 2008, and millions of YouTube viewers later saw Pogan shoving the cyclist off his bike; the officer said he was defending himself.

Pogan faces up to four years in prison at his sentencing, set for Wednesday.

The Times Square episode happened only a week after London came across Harvin, then 28, walking into his mother's apartment building without a key.

London and another officer followed Harvin to the elevator and confronted him. Then London began to hit Harvin in the head and elsewhere with a baton, ultimately delivering nearly 20 blows to the unarmed and eventually handcuffed man.

Many of them landed as Harvin was on the floor, trying to cover his body to defend himself, the video shows. Harvin suffered cuts and bruises.

London submitted reports saying Harvin had repeatedly kicked and punched the officers, and Harvin was arrested on resisting-arrest and disorderly conduct charges. They were dropped after prosecutors saw the videotape, shown in court Friday.

"To justify his conduct, officer London makes up a story about how Harvin was attacking him," Manhattan Assistant District Attorney David Drucker told jurors in his opening statement. Through the video, he said, "You'll see exactly what happened."

He said the silent video didn't record verbal threats Harvin had made to London. Harvin was still struggling against the officers after being handcuffed, Worth added.

"(The video) is not going to give you all the context, I submit, that you need," Worth said. "This is not an assault. This is the use of necessary force in order to make an arrest."

Jurors are unlikely to hear from Harvin, as prosecutors have said they now can't find him.

The Army veteran has behaved somewhat erratically since he returned from Iraq with post-traumatic stress disorder, and his encounter with London exacerbated his emotional problems, said his lawyer, Adam M. Orlow. He said Friday he hadn't heard from Harvin in two months.

"I wish he'd be here for the criminal trial, but he is suffering from this," Orlow said.

Harvin has filed a $35 million federal civil-rights suit against London and the New York Police Department.

London, a 16-year NYPD veteran, has been assigned to administrative duties since the incident. If convicted, the 45-year-old officer faces up to seven years in prison.